BRUSSELS--The United States and its NATO allies signalled a willingness on Thursday to consider slowing their withdrawal from Afghanistan, days after the Taliban's brief takeover of a provincial capital stoked concern about the strength of Afghan state forces. U.S. Defence Secretary Ash Carter said he asked allies for flexibility as Washington reviews a withdrawal timetable currently supposed to slash the nearly 10,000 U.S. troops to a small U.S.-embassy based force after 2016. "A number of countries today indicated a willingness to change their plans and posture," Carter said after a NATO defence ministers meeting in Brussels. NATO says there are more than 6,000 non-U.S. forces contributing to the "Resolute Support" mission. NATO Secretary-General Jens Stoltenberg told reporters flatly: "I sense that many allies are willing to stay longer if needed." Although Afghan forces have recaptured the strategic northern city of Kunduz, its brief fall to the Taliban last month underscored concerns about the capabilities of Afghanistan's security forces. U.S. President Barack Obama had aimed to withdraw all but a small U.S. force before leaving office, pinning his hopes on training and equipping local forces to contain Taliban militants fighting to return to power. Washington has spent around $65 billion on preparing the fledgling Afghan security forces of about 350,000 personnel. But that is still very far from complete. Carter said he was preparing a U.S. funding request to sustain Afghan troops at their target peak levels of around 350,000 in 2017 "and beyond". The political perils of the Afghan mission came into stark view after a U.S. military strike on Saturday in Kunduz hit an Afghan hospital run by Doctors Without Borders, or Medecins Sans Frontieres (MSF). Obama on Wednesday apologised to MSF for the bombing, which killed 22 people, and came as Afghan forces, with U.S. support, fought to retake the city. Germany's defence minister said NATO troops may need to stay longer and pointed directly to the fighting in Kunduz. "We'll need to look at how we go forward and whether we should stay longer," Ursula von der Leyen told reporters.